Aspirated smoke detectors draw air from a variety of locations via a fan thru a piping system into a common detection chamber. The piping system has several holes in different locations thru which smoke/air will be drawn to the smoke detector.
Representative detectors are disclosed in published U.S. patent applications such as 2010/0271219 published Oct. 28, 2010, entitled “Variable Air Speed Aspirating Smoke Detector”, and 2015/0022363 published Jan. 22, 2015, entitled, “Multi-Channel Aspirated Smoke Detector”. The '219 and '363 applications are assigned to the assignee hereof and are incorporated herein by reference.
Aspirated smoke detectors are often used in industrial settings such as coal mines or flour mills. In such environments there can be extensive airborne pollution in the form of airborne particulate matter. Such detectors need to be protected against air pollution.
Known detectors often include a built-in filter. But there are many applications where the air is so polluted that a pre-filter with an easy changeable filter medium needs to be installed. There are some pre-filters on the market for use with aspirated detectors. However, if the filter medium is missing because it was taken out, for example because of being dirty, and in need of replacement, and if not promptly replaced then polluted air can flow into the detector and the sensing chamber.
There is a need to address the deficiencies of known pre-filters.